The invention relates to a connecting element, in particular a screw or a bolt, for connecting two bodies.
For electronic systems in motor vehicles, at connecting points between two components or bodies in which a force is concentrated, there is increasing demand for a small and compactly designed force sensor that can be produced inexpensively and in mass quantities. This is particularly true for the measurement of the weight acting on the seat of a motor vehicle and the weight distribution or changes in the weight as a function of time. There is also an increasing demand for precise, statically measuring force sensors in production measuring methods and quality measuring methods.
Small, known sensors are mostly based on the piezoelectric converter principle and can therefore only be operated dynamically. By contrast, static force sensors are frequently embodied as bending springs, which, equipped with strain gauges, do in fact produce very precise force sensors, but they are relatively large in size and are comparatively expensive.
In addition, magnetoelastic sensors are known, which are either based on the Kreuzduktor principle, which is particularly suitable for applications, which must function without electronics on site due to high temperatures or in which there is only a small amount of space available, or which are based on the Torduktor principle, in which two U-shaped cores, which are rotated in relation to each other by 90xc2x0 and wound with coils, detect the magnetic field distribution in a contactless, force-dependent manner.
The Kreuzduktor principle has the disadvantage that it only supplies low useful voltages, which are more often than not encumbered with a large offset and can therefore only be evaluated with difficulty. In addition, they can only be used at a high additional cost when there are moving or rotating parts. The Torduktor principle does permit force measurements to be executed on rotating parts as well, but is very distance-sensitive.
The object of the invention was to produce a small, compactly designed force sensor in the form of a connecting element, which permits in particular a reliable seat weight sensing in the seat of a motor vehicle. In this connection, the force sensor should not increase the seat height and should produce a fixed stop in the event of an overload.
The connecting element according to the invention has the advantage over the prior art that it can be easily adapted to different measurement ranges by means of different cross sectional diameters of the inserted shaft and the geometry and dimensions of the slot let into the shaft.
The connecting element according to the invention can also be embodied as very small and compactly designed and it uses a static measuring principle. In this respect, it can be universally used to measure the connecting forces between two parts.
An additional advantage of the connecting element according to the invention lies in the fact that the magnetic field generated can be picked up in a force-proportional and contactless manner in the air gap produced by the slot and by means of the magnetically sensitive element disposed in the vicinity of this air gap. In this connection, it is particularly advantageous that even a slight change of the form or width of the slot due to the action of an external force or a mechanical strain at the location of the magnetically sensitive element by means of the component that produces the magnetic field causes an intense change in flux density. As a result, even slight changes in the form of the slot produce a powerful measurement signal.
In the connecting element according to the invention, it is also advantageous that the magnetically sensitive element can be fully integrated with an associated set of evaluation electronics in it, which permits a simple supply and a compact, extremely inexpensive construction.
Another advantage of the connecting element according to the invention, particularly in its embodiment as a force measuring screw or force measuring bolt on the seat of a motor vehicle, is the possibility of also executing a belt force sensing, for example at the point at which it is anchored to the seat of the motor vehicle.
It is particularly advantageous if an intrinsically known Hall sensor element is used as the magnetically sensitive element, whose primary advantage is its favorable zero point stability.
On the other hand, in the case of the magnetic measuring method used, it is advantageous that the magnetically sensitive element is disposed in the magnetic zero point and therefore also a possible aging of the magnetic circuit or of the component that generates the magnetic field does not contribute to the offset of the Hall sensor element.
Through the additional provision of conventional strain gauges, it is also possible in a simple manner to differentiate between a tensile strain acting on the connecting.
Drawings
The invention will be explained in detail in conjunction with the drawings and in the subsequent description.